I'm posting this info as an announcement to keep it handy. I had the easy job... all the heavy lifting was done by revdocdrew. Thanks, Drew.

--16ga.

PROOF/PRESSURE

British proof markings: The "tons" mark (which is service pressure) was not used until 1954. Between 1925-54, the chamber length was marked. 1904-1925 guns would not have the chamber length, but only the shot charge and a nitro proof.
http://www.gunproof.com/Proofing/proofing.html

There are three pressure measurement systems (lead crushers/LUP, copper crushers, and piezo), and two standard systems of measure units (USA/SAAMI and CIP/British/European) and two differing units (psi and tons and bar and Kg/Cm sq) within each system, different proof laws by country, and differing proof laws by age.
Unfortunately, there is essential NO formula to convert BAR expressed as LUP (CIP) to PSI (SAAMI). LUP + 1000 does not reliably predict the actual piezoelectric transducer measured pressure.
In 1989, all proof data was marked in metric using the BAR as the unit of measurement. The use of TONS per sq. inch was dropped. Under this system, 850 bar represented standard proof, with 1200 bar being special or magnum. 2 1/2" chambered guns are usually proofed 850 bar
2 3/4" chambered may be proofed 900 bar (3 1/4 tons per sq. inch) or higher.

**650 bars is standard CIP (British and European) service pressure for shells designed for guns proofed at the CIP standard of 850 bars**

Baschieri & Pellagri data BUT you must add 500-1000 psi to the reported pressure to get an approximation of the SAAMI equivalent PSI. The 16g F2 Classic is factory listed at 9,867 psi but testing by Tom Armbrust showed it to be 10,500.
http://www.bandpusa.com/files/db_trio.pdf

Gamebore Traditional Game 16g 28gm (1 oz.) is reported to run 1260 fps at 8122 psi but pressure testing by Tom Armbrust showed it to be 8400 psi. The box is labeled "These cartridges are suitable for use in:
70mm case length: Guns with a chamber length of 2 3/4" or longer, nitro proofed to a service pressure of 3 1/4 tons per square inch (900 kg per square cm)
67 mm case length: Guns with a chamber length of 2 1/2" or longer, nitro proofed to a service pressure of 3 tons per square inch (850 kg per square cm.)"

It's appropriate to view the 3 ton/650 bar/8,939 psi pressure as the maximum service/using pressure rather than the standard/recomended service pressure. The Gamebore loads run below 8500 psi but are 'approved' for use in 3 ton/650 bar service/850 bar proof guns. In light of the age of the wood and metal of classic American and British SxSs, shoot low pressure to save the action, shoot light shot charge/low velocity to spare the wood. It seems reasonable to limit pressure to 8,500 psi, and several commercial loads are available from 5,000- 7,000 psi http://www.doublegunshop.com/forums/ubbt...ge=11#Post31805

BOTTOM LINE: ANY 850 BAR (proof) = 650 BAR service or 3 TON service gun should be fine at pressures under 8500 psi, or 3 1/4 tons less than 9,500 psi.

Vic Venters discusses Britain's Rules of Proof at length in the Jan/Feb 2009 issue of Shooting Sportsman. The service pressure conversions per the 1954 Rules as stated above are correct but the psi is as measured by CIP radial-transducer rather than the SAAMI piezoelectric method.